JPS60254747A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To decrease bird's beaks without making an initial oxide film thin, by heat-treating the initial oxide film, which is formed on a semiconductor substrate in an NH3 atmosphere. CONSTITUTION:A silicon dioxide film 2 (an initial oxide film) is formed by thermal oxidation on a silicon substrate 1 to the thickness of 500Angstrom . Then heat treatment (annealing) is performed in an NH3 atmosphere for 60min at 1,100 deg.C. Thereafter, a silicon nitride film 3 (a nitride film) is deposited on the film 2 by, e.g., a chemical vapor growing method to the thickness of 1,000Angstrom . Then, the patterning of the nitride film 3 is performed. Thereafter, a field oxide film 4 is formed by heat treatment in an wet oxygen atmosphere at 900 deg.C. Finally the nitride film 3 and the initial oxide film 2 are removed by the etching on the entire surface. In this method, the width of the bird's beak, which has been 0.5-0.6mum in the conventional device, can be reduced to 0.3-0.4mum. This fact is very effective for high integration of the semiconductor device.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of reducing bird's beak in a LOGOS process.

(Background of 2-layer technology) The LOGO5 process for forming a field oxide film for active region isolation in the manufacture of semiconductor devices will be explained with reference to the cross-sectional view of Figure 1. A silicon dioxide (5iO2) film 2 is formed on the substrate 1 by thermal oxidation at, for example, 1000° C. to a thickness of several hundred nanometers (this oxide film is called an initial oxide film), and a silicon nitride film 3 ( A Si3Ng film (hereinafter abbreviated as nitride film) is grown by, for example, chemical vapor deposition (CVD).
It can be applied to a film thickness of 1,000 to 1,500 people using the method.

Next, as shown in the same figure (bl), the nitride film 3 is patterned.

Next, a field oxide film 4 is formed to a thickness of 6,000 to 7,000 wafers by heat treatment in a humid oxygen atmosphere at 900 DEG C. (FIG. 4(C)).

Finally, the nitride film 3 and the initial oxide film 2 are removed by etching the entire surface (FIG. 4(d)). Figure 1 (The part above the dotted line of the field oxide film 4 in C1 was the initial oxide film, but since it was etched, the field oxide film 1*4
becomes thinner by that amount.

Here, when comparing FIG. 1(b), (C1, and (d)), the area of the field oxide film 4 is shown by the dotted line I in FIG. 1(b),
The settings were made as shown by I, but at stage C1 (this stage is hereinafter referred to as no full surface etching), the field oxide film has spread to the area indicated by dotted lines ■ and ■. At the stage dl (this stage is referred to as full-surface etching below), the field oxide film has shrunk to the point indicated by dotted lines ■ and ■ in the figure, but this dotted line I
The part between and ■ is called the bird's beak.

An active region exists next to the field oxide film 4 as an isolation region as shown in FIG. 1(d),
Elements such as transistors are made there,
Since the active region becomes narrower by the size of the bird's beak, research is being conducted to reduce the size of the bird's beak. In FIG. 1(d), 5 and 6 are the source and drain, and 7
8 represents a gate oxide film, and 8 represents a gate electrode.

(3) Prior Art and Problems It is known that in the conventional LOGO3 process, bird's beak can be reduced by making the initial oxide film thinner. Figures 2 and 3 are diagrams showing the relationship between the initial oxide film thickness (taken on the horizontal axis) and the bird's beak (taken on the vertical axis).
The figure shows the stage shown in Figure 1 (C) without the entire surface etching, and Figure 3 shows the state shown in Figure 1 (dl) with the whole surface etched. The above relationship is shown.

However, if the initial oxide film is thinned, there is a problem that the substrate silicon may be damaged during etching of the nitride film.

(4) Purpose of the Invention In view of the above conventional problems, an object of the present invention is to provide a method for reducing bird's beak without thinning the initial oxide film.

(5) Structure and object of the invention According to the invention, there is a step of forming an initial oxide film on a semiconductor substrate and heat-treating it in an NH3 atmosphere, and forming a film on the oxide film to serve as a mask for the next heat treatment. This is achieved by providing a method for manufacturing a semiconductor device, which includes the steps of forming and patterning the substrate and heat-treating the substrate to form an active region isolation oxide film.

(6) Examples of the invention Embodiments of the present invention will be explained in detail below with reference to the drawings.

The method of the present invention is carried out in the following steps.

First, as in the conventional case, an initial oxide film is formed to a thickness of 500 nm.

Next, heat treatment was performed at 1100°C for 60 minutes in an NH3 atmosphere (
annealing).

Thereafter, a nitride film is grown to a thickness of 1000 nm as shown in FIG. 1 (al) in the same manner as in the conventional method.
.

This is done in the same way as in the conventional case described with reference to (d).

The results of implementing the method of the invention are shown by curves B and D in FIGS. 2 and 3. Previously, the bird's peak width was 0.5
~0.6 μm, but according to the present invention, it is 0.6 μm.
It was demonstrated that the thickness was reduced to 3 to 0.4 μm, which is extremely effective in increasing the integration of semiconductor devices.

(7) Effects of the invention As explained in detail above, according to the present invention, highly integrated LSI
Bird's beak, which was the most serious problem in semiconductor devices, can be reduced, and this can be achieved without damaging the silicon substrate, which is highly effective in not only increasing the degree of integration of semiconductor devices but also improving their reliability.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the LOGO5 process, and FIGS. 2 and 3 are diagrams showing the relationship between the initial oxide film thickness and bird's beak. 1-Silicon substrate, 2-Initial oxide film,

Claims (1)

[Claims] A step of forming an initial oxide film on a semiconductor substrate and heat-treating it in an NH3 atmosphere, a step of providing a film to serve as a mask for the next heat treatment on the oxide film and patterning it, and a step of heat-treating the substrate to separate active regions. 1. A method of manufacturing a semiconductor device, the method comprising the step of forming an oxide film.